1. Field of the Invention
The present invention relates to a mark detecting method of detecting a mark for indicating a crystal orientation as formed on the outer circumference of a wafer such as a semiconductor wafer, and more particularly to a mark detecting method of detecting a mark of a large-size wafer having a diameter of 450 mm.
2. Description of the Related Art
Usually, a mark for indicating a crystal orientation is formed on the outer circumference of a wafer, and a wafer processing direction as in a cutting apparatus is decided in consideration of the crystal orientation indicated by the mark. As a conventional mark detecting method of detecting such a mark, there is a method of simultaneously detecting the center of a wafer and the mark for indicating the crystal orientation of the wafer by imaging the outer circumference of the wafer (see Japanese Patent Laid-open No. 2011-40637, for example). In the mark detecting method described in Japanese Patent Laid-open No. 2011-40637, the whole of the outer circumference of the wafer held on a holding table is imaged by an imaging apparatus. Thereafter, the center of the wafer is calculated from the image obtained by the imaging apparatus, and the mark is detected from a change in position on the outer circumference of the wafer.